In the field of coal gasification it is advantageous to feed coal into a high temperature gasifier at pressures up to 100 atmospheres or more. One system used heretofore is to use a slurry feeder. However, these feeders required a slurry, which was dirty or difficult to handle, or they are were otherwise troublesome or hard to operate effectively. To overcome these problems it was proposed to use lock-hoppers, but these systems were inefficient heretofore, since the loading operation caused the lock-hoppers to fill with high pressure gas when the coal was dumped, and then to be released to the ambient atmosphere every time the hoppers were opened for refilling. Additionally, they were expensive to build and operate since they required expensive seals, which were subject to rapid wear and/or replacement because they were subject to abrasion from the solid passing through the lock-hopper.